Supplement to "Nature" November 6, 1902. 



an exact date for Thothmes III. from under your hat. 

 "Astronomical evidence," says Dr. Budge (i. p. 158), 

 "supports the evidence derived from every other source 

 in assigning a remote antiquity to the period when 

 Egyptian civilisation began ; but unfortunately it does 

 not assist us in formulating a complete system of 

 Egyptian chronology with exact dates." 



Altogether the work is of great interest, and will no 

 doubt prove of use to the scientific student as well as to 

 the lay inquirer ; and it is a monument to the*industry of 

 its author. 



MOHR ON THE DYNAMICAL THEORY OE 



HEAT AND THE CONSERVATION OF 



EN ERG 1 '. 



Die Entwickelung unserer Naluranschauung in XIX. 



Jahrhundert unci Friedrich Mohr. By Ch. Jezler. Pp. 



44 and portrait of Mohr. (Leipzig : Barth, 1902.) 



Price 1.20 Mark. 



MOHR, the apothecary and chemist, is a name that 

 will ever be associated with the foundation of the 

 methods of volumetric analysis. Mohr as a contro- 

 versialist in the domain of speculative geology is not so 

 generally known, and Mohr as a pioneer in connection 

 with the dynamical theory of heat and the doctrine of 

 the conservation of energy is so little known that his 

 writings have had to be rescued from oblivion by the 

 author of the present pamphlet. 



The work under consideration formed the subject of 

 a communication to the Society of Natural Science at 

 Winterthur in December, 1900, and while the paper was 

 being prepared for publication there appeared in the 

 Berichte of the German Chemical Society for April, 1900, 

 the " Reminiscences of Friedrich Mohr," by Hasenclever, 

 who knew Mohr personally, and who deals more par- 

 ticularly with his correspondence with Liebig. It 

 appears, however, that one of the two most important 

 works published by Mohr in 1837 escaped the notice of 

 Hasenclever, and it is upon this particular work that Herr 

 Jezler more especially bases Mohr's claim for prominent 

 recognition among the founders of modern science. 



The pamphlet which has been submitted for considera- 

 tion is certainly worthy of very careful attention by all 

 who are interested in tracing the history of one of the 

 greatest generalisations in physical science of the nine- 

 teenth century. The first section deals with the develop- 

 ment of science as a whole, and is to be regarded as a 

 kind of background in which the figure of Mohr is 

 framed. The second part gives the detailed account of 

 Mohr's work with copious extracts from his published 

 papers, some of the early communications to the first 

 volume of Poggendorff's Annalen having given the author 

 no little trouble to obtain on account of their scarcity. 

 The general impression which the reader must form is 

 that Mohr's claim to take high rank among the scientific 

 worthies of the past rests on a very much broader basis 

 than has generally been conceded. Passing over the 

 evidence of his many-sided activity in other departments 

 of science, it is unquestionably in connection with the 

 development of the modern conceptions of heat as a kind 

 of motion and of the "unity of forces" (Einheit der 

 Naturkrafte) that the greatest interest will be aroused. 

 NO. I723, VOL. 67] 



In order to fit Mohr into his proper place, the author 

 expands the three scientific achievements of the past 

 century as classified by Haeckel into four : — (1) The 

 doctrines of the indestructibility of matter and energy ; 

 (2) the theory of the correlation or unity of natural 

 forces ; (3) the establishment of chemistry as an inde- 

 pendent science ; and (4) the development of physiology 

 and biology and the Darwinian theory. There is, perhaps, 

 scope for criticism in the proposed classification, but it is 

 not essential to the author's main contention whether 

 this scheme be rigidly adhered to or not. It will suffice 

 to mention that under each of the four headings he gives 

 a brief historical resume. The treatment is necessarily 

 very scrappy, owing to the small amount of space which 

 the author has allowed himself considering the enormous 

 field which he has had to cover. It is clear, however 

 from the facts submitted under the heading of " the 

 theory of the indestructibility of force" and elaborated in 

 detail in the second part of the work that Mohr's views 

 were formulated with considerable precision and pub- 

 lished some five years before R. Mayer's first paper on 

 this subject in 1842. In chronological order, Herr Jezler 

 therefore names in connection with this generalisation 

 Carnot, Mohr, Mayer, Joule, &c. 



A somewhat acrimonious (and unscientific) controversy 

 raged in this country many years ago respecting Mayer's 

 claims to priority. The writer of this notice has not the 

 least desire to stir up the ashes of this dead strife, but 

 admitting Mayer's claims, it is interesting to learn from 

 the pamphlet before us that Mohr himself drew Mayer's 

 attention to his earlier publications and that a corre- 

 spondence took place in the course of which Mayer 

 wrote : — 



" In dem wichtigen und sehr geistvollen Aufsatze, 

 welchen Sie in ihrem neuesten Werke ' Die mechanische 

 Theorie der chemischen Affinitat' zitieren, haben Sie 

 unstreitig die mechanische Warmenlehre ausgesprochen 

 und haben sogar das Warmaquivalent numerisch zu 

 bestimmen gesucht." 



The reference which Mohr makes in this later work 

 quoted by Mayer is to his first paper of 1837, entitled 

 "Ansichten uber die Natur der Warme" {Annalen der 

 Pharmacie, vol. xxiv. p. 141). In this same letter it may 

 be mentioned that Mayer claims priority over Joule in 

 the determination of the mechanical equivalent of heat. 

 Mohr's second paper of 1S37 is entitled " Ueber die 

 Natur der Warme," and a quotation from this paper given 

 in the present pamphlet (p. 10) shows that Mohr had 

 fully realised the principle of the "correlation of the 

 physical forces," as it was afterwards called by Grove in 

 his celebrated work bearing this title. The historian 

 of this branch of physical science, Max Planck (" Das 

 Prinzip der Erhaltung der Energie," Leipzig, 1887), in 

 pushing Mohr's claim, appears also to have depended 

 only upon this second paper and to have overlooked the 

 first paper. Reading this contribution now in extenso as 

 it is reprinted in the pamphlet, it is remarkable to find 

 how closely Mohr approximated in the year 1837 to the 

 current views held by physicists and chemists. The 

 subject was certainly in the air, but Mohr was apparently 

 too far in advance of the time, for his papers fell into 

 oblivion until he himself reminded his contemporaries of 

 their existence. As is pointed out, however, in the 



